This invention relates generally to telecommunications networks, and more specifically to the integration of voice and data transmissions over such networks.
A typical telecommunications network is comprised of a central office (CO) and a connecting network called a local ring. The CO contains the necessary switching equipment and the local ring is the intermediate network between the CO and the end-user. The topology of the network is a ring structure. A local ring may be a fiber network that may typically employ the synchronous optical network (SONET) standard for transmitting digital information. SONET defines a hierarchy of interface rates for different fiber-optic transmission systems to allow data streams at different rates to be multiplexed. Employing the SONET standard makes it possible for communication carriers to interconnect existing digital carrier and fiber-optic systems.
FIG. 1 shows an example of a typical local ring. The telecommunications system 100, shown in FIG. 1, includes a CO 105. Each CO 105 has a number of local ring networks 110 connected to it. The number depends on the service area and the physical size of the CO and is typically less than a hundred. Local ring network 110 is a fiber-optic ring network connecting the CO to the end-user via remote terminals (RTs). Along the local ring network 110 are a plurality of RTs, for example RTs 115a, 115b, and 115c that are located throughout the service area. In a typical system there may be between ten and one hundred RTs connected to a given CO. The RTs contains circuitry that will span out copper wire 120 to the end-users in the vicinity of the RT.
The ring topology of the SONET based system 100 provides for fast failover in the event that the fiber-optic local ring network 110 experiences a failure (i.e., is unable to conduct data traffic). The local ring network 110 implements a dual counter-rotating ring so that if a break occurs in one ring the data traffic is shunted to the other ring. That is, the data flows in the other direction. For example, suppose data flows from RT 115b to CO 105 by way of RT 115a. If a break occurs in local ring network 110 between RT 115a and CO 105, data from RT 115b is directed to CO 105 by way of RT 115c. The SONET standard requires that this failover occur within 50 milliseconds (ms).
A SONET based network having ring topology presents several difficulties related to high speed data transfer as described below.
The ever-increasing importance of Internet access in our daily lives has led to increased emphasis on low-cost/high speed Internet connectivity.
Ethernet is one example of a technology that provides high-speed data access. Ethernet is a data transmission technology for local area networks (LANs). Ethernet may transmit data over a fiber-optic cable at rates up to one gigabit per second or higher. Ethernet transmission systems are LAN-based and transmit broadcast packets. On an Ethernet LAN, transmission points compete for the ability to use the shared network paths at a given time. If too many transmissions are attempted at one time the overall performance may be affected. To avoid this, an Ethernet network may be divided into segments with a device called a bridge connecting any two segments. Therefore, an Ethernet network should not operate on the ring topology of current SONET based networks. That is, the broadcast packets would continue around a ring.
A Digital Subscriber Line (DSL) is another technology that provides high-speed data access. The cost is low because DSL works on existing copper telephone wires obviating the need for costly installation of higher-grade cable. Signals from multiple DSL connections are sent to a DSL access multiplexer (DSLAM) for routing through a high-speed backbone (e.g., asynchronous transfer mode (ATM)). The DSLAM is typically located at the CO. Therefore, the farther the end-user is from the CO, the lower the speed due to the length of the copper wires. Eventually a point is reached (approximately 3 miles) where the CO cannot provide DSL service at all.
Current SONET systems do not support load sharing, the ability to shunt data traffic to another transmission path if congestion occurs or data transmission rate exceeds the maximum for a given transmission path.
A method is disclosed wherein a local ring telecommunications network is segmented using VLANs. At least two unique VLANs are used to partially traverse the ring forming two logically separate networks where each device on the ring has access to both VLANs. In the event of a break in the ring, devices failover to the alternate VLAN traversing the functional remnant of the ring. Load sharing also occurs between VLANs allowing each device an optimum path for traffic to traverse the ring. Other features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description, which follows below.